From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.5-pre1 Path: eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!nntp-feed.chiark.greenend.org.uk!ewrotcd!newsfeed.xs3.de!news.jacob-sparre.dk!franka.jacob-sparre.dk!pnx.dk!.POSTED.rrsoftware.com!not-for-mail From: "Randy Brukardt" Newsgroups: comp.lang.ada Subject: Re: Proposal: Auto-allocation of Indefinite Objects Date: Sun, 9 Aug 2020 19:31:06 -0500 Organization: JSA Research & Innovation Message-ID: References: <94a54092-a56f-4a99-aaec-08dd611c8fd8@googlegroups.com> <8a502b6c-4609-4cd8-b292-5797fe6421e1n@googlegroups.com> Injection-Date: Mon, 10 Aug 2020 00:31:07 -0000 (UTC) Injection-Info: franka.jacob-sparre.dk; posting-host="rrsoftware.com:24.196.82.226"; logging-data="4397"; mail-complaints-to="news@jacob-sparre.dk" X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 X-RFC2646: Format=Flowed; Response X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.7246 Xref: reader01.eternal-september.org comp.lang.ada:59694 List-Id: "Dmitry A. Kazakov" wrote in message news:rfs7k4$c83$1@gioia.aioe.org... > On 29/07/2020 17:33, Brian Drummond wrote: >> On Tue, 28 Jul 2020 16:59:09 +0200, Dmitry A. Kazakov wrote: > >>>> A constant String := "done"; >>>> Q : indefinite String; >>>> ... >>>> loop >>>> Q := Get_Line; >>>> exit when Q = A; >>>> end loop; >>> >>> I am not comfortable with the semantics of this and with possible >>> implications too. I would keep it simple. >> >> Interesting. Can you pin down some of that discomfort? It looks simple to >> me : >> >> "indefinite" indicates the size can vary (and the compiler knows whether >> it used the heap or stack), and in the absence of "aliased" we know there >> are no copies of the pointer (if heap). > > I don't like compiler relocating objects. If the pool is a stack (or heap > organized as a stack) it might be unable to do this. This is not that hard to deal with. Janus/Ada handles discriminant-dependent components of mutable objects this way: they are allocated on the stack, but if they have to be reallocated they move to the heap. I note that the original idea already exists for discriminant-dependent components -- that's a bit more painful to use but hardly difficult. The main issue is that most compilers fail to support these components properly, using some sort of max-size implementation unconditionally rather than switching to a pool-based implementation when the max size is too large. I've never understood why Ada compilers were allowed to make such a limitation (it becomes a major limitation when working on non-embedded programs), while similar limitations on case statements and aggregates are not allowed. Randy.